Cyrix-Li-ct 120A schematic shows short condition in Start Assistant

DIY
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1

Looking at the Cyrix Li-ct data sheet again, The connect logic says:
“The Cyrix-Li-ct will parallel connect a lead acid starter battery and a LiFePO4 battery: - if the Charge Disconnect output of the VE.Bus BMS is high”
So the yellow line is High.

In the diagram, the start assist switch only connects that pin to ground and does not disconnect BMS Charge.

so I am reading that BMS High is being sent to ground.

I am not using the victron bms controllers, so my BMS charge is straight 12v. And connecting those two is sparks.

Is there something I’m missing?

Thanks
A

Screenshot 2026-09-19 at 7.13.12 PM
Screenshot 2026-09-19 at 7.13.12 PM1402×864 104 KB

2

Yes, you are missing that the Victron BMS is designed for that. :wink:

But disconnecting 85 twice shortly has the same effect.

3

Start assist function: a short negative pulse will close the relay during 30 seconds…

BMS charge most likely pulled to 12V through a resistor. (Wired-OR).
A small light in series with your 12V connection might also work.